Fix incorrect member variable (#76)

Summary:
Pull Request resolved: #76

This variable doesn't exist. It's supposed to be `weight`. This was flagged when building with llvm-19

Reviewed By: yozhu, jeongseok-meta

Differential Revision: D62666886

fbshipit-source-id: 642b9150636ec7733be4d8f2851333e56726e615

momentum/character_solver/vertex_error_function.h

@@ -26,7 +26,7 @@ struct VertexConstraintT {
   VertexConstraintT<T2> cast() const {
     return {
         this->vertexIndex,
-        (T)this->weight_,
+        (T)this->weight,
         this->targetPosition.template cast<T2>(),
         this->targetNormal.template cast<T2>()};
   }